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Toybox Lid Warping--help!

12-22-2007, 02:24 PM

I edge glued three 3' x 3/4" x 4" pieces of solid poplar to make a toybox lid. It was perfectly flat when unfinished. My wife (designated painter) painted the underside of the lid with three coats of latex enamel a couple of days ago, and flipped it over yesterday today to paint the top. I noticed that that the short edge is severely cupped...it has almost a 1/4" gap in the middle (see picture).

Can painting one side of a hardwood panel warp the wood that much? The top side is still drying and still needs a third coat...is there any hope that it will dry and straighten it out?

I'm delivering it after Christmas...I'm now debating whether I need to redo the lid this weekend.

I edge glued three 3' x 3/4" x 4" pieces of solid poplar to make a toybox lid. It was perfectly flat when unfinished. My wife (designated painter) painted the underside of the lid with three coats of latex enamel a couple of days ago, and flipped it over yesterday today to paint the top. I noticed that that the short edge is severely cupped...it has almost a 1/4" gap in the middle (see picture).

Can painting one side of a hardwood panel warp the wood that much? The top side is still drying and still needs a third coat...is there any hope that it will dry and straighten it out?

I'm delivering it after Christmas...I'm now debating whether I need to redo the lid this weekend.

Yes it can. You are sealing off the wood on one side only.

How is your end grain? If you look at the edge are the "circles" all facing the same direction (I would say they are to the top from the looks of your picture) They should alternate, but that is not always foolproof either.

The only way I can see to save that one is to cut it into 3 again (carefully because it wont be flat on the saw table) and flip either your inner or 2 outer boards over. When you refinish it, do the back side, then let it dry and get a coat on the top before you finish the back so they are going on evenly

Comment

I would do as OA stated but finish both sides at the same time. Make a support for your top using some scrap plywood and drive finish nails up through the plywood. Put the plywood down with nail points facing up so that your top can rest on the points of the nails. Then paint the bottom first, flip it over on top of your plywood support, then paint the top so that both sides will dry at the same time. By painting 3 coats on one side first as you have done you are adding alot of moisture to one side as the other side is trying to dry causing it to cup as it has.

I don't remember the endgrain pattern, but I could very well have joined them in a non-alternating fashion--the paint is hiding it now...

One other idea I have....screwing some poplar support rails (3/4" x ~2") on the underside of the lid, as a "new design feature". I'm hoping that will straighten it out. I've seen some pictures of toyboxes with these rails, so it's not unprecedented.

If it doesn't work, I may have to run and get a prejoined pine panel from Lowes....sigh.

Comment

I would first paint the bottom. Latex paint has a lot of water in it. When you painted the top, it was like soaking it with a rag, and the wood expanded. When you do the bottom, hopefully it will equalize. In the future, do both sides as Nailbanger said.
If you put cross braces on it, make sure all the screw holes except one are oversized or elongated, so the top can expand and contract. If it is hinged at the back and the cross rails are inside the box, the hole closest to the hinge should be the tight hole, and that is also the end to glue if you decide to. This will keep the rail indexed to the hinge when the top expands.

Good luck.

Go

Practicing at practical wood working

Comment

Every toybox or chest I've made I put 2 cleats on the inside of the lid.
It is not uncommon to do this. I've seen many chests without cleats that warp or break. People tend to slam lids or sit on them or stand on them, the cleats are mandatory in my opinion.

Comment

I'm sure that painting one side several days before the other is the biggest culprit in this. It may have happened anyway, maybe to a lesser degree though, had both sides been painted at once. The cross grain runners would likely have done more good if they had been applied before painting. Once the warp has happened, you are taking a big risk. Forcing the piece flat may very well split it.
Plywood with a hardwood edgeband would solve this perminently. It would stand abuse far better too.

Comment

I do not know if you have ever noticed the Back relief cuts on trim flooring and molding, but part of the reason they are there is to help reduce warpage, and how they work is to cut the surface of the lumber, removing the surface movements, that can pull or expand and warp the materials,

on large lids and panels many times can benefit from a similar treatment by scoring or "veeing" some lines in the back of the panel thus the board starts to work more like individual narrow boards, (not that it can not warp but the effect is usually less), they do not necessarily need to go through to the ends. (a vee cutter in a router) or a table saw with stops will work, the lines are usually with the grain.

also when finishing a project do both sides at once, if you need to on the bottom side put a few finish nails in it and when done finishing it, flip it over on the nails and continue on the top side.

when one is doing High grade laminate work or if you notice laminated or plastic printed on panels both sides will be done, (uslay the back side is just what is called a backer) but it is to give the panels the same surface tension, so they do not warp,

Push sticks/blocks Save Fingers
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